There are generally two types of single-substrate substrate surface processing apparatus. In one form thereof, a substrate surface processing medium, such as a plasma, is controllably produced by two electrodes in a diode configuration, and in another form thereof, the substrate surface processing medium is controllably produced by three electrodes in a triode or other three-electrode configuration. For such machines, one or more selected surface processing media are caused to interact with suitably prepared surfaces of semiconductor wafers or other materials to form intended microstructures thereon and/or to remove unwanted residues therefrom that remain from one or more prior substrate surface processing steps. The model "384" diode reactor, commercially available from the instant assignee, and the model Wafer Etch 606/616 Triode Reactor, commercially available from GCA Corporation, are among the diode and triode reactors known to those skilled in the art. For the diode reactors, the substrate surface processing medium, such as a plasma, is controllably produced between the two electrodes in the diode configuration, while in the triode reactors, the substrate surface processing media, such as plasmas, are controllably produced between the upper electrode and the grid electrode on the one hand and between the grid electrode and the lower electrode on the other hand.
There are generally two types of substrate surface processing media controllably produced by the single-substrate substrate surface processing reactors in either the diode or triode configurations. For some types of substrate surface processing, such as for etching oxide or other materials on semiconductor wafers or other substrates, these reactors produce substrate surface processing media constituted principally by selected ions, while in other types of substrate surface processing, such as for chlorine etching of aluminum or other materials on semiconductor wafers or other substrates, these reactors produce substrate surface processing media constituted principally by certain selected chemical species. The former type of processing is known as "ion-dominated" processing while the latter type is known as "chemically-dominated" processing. Ion-dominated and chemically-dominated processing, in dependence on the specific microstructure being formed and on the phase of the overall fabrication process, may controllably effect either a build-up on (deposition, growth and the rest) or a removal from (etching and the rest) the surface of the substrate.
The utility of the heretofore known reactors in either the triode or diode configurations for both ion-dominated and chemically-dominated processing has been limited in respect to the degree of uniformity of substrate surface processing able to be obtained. In the application to very large scale integration (VLSI), for example, where more integrated circuits are being fabricated on ever larger semiconductor wafers, the effective yield of manufactured devices depends on the degree of uniformity obtained by the substrate surface processing apparatus. As the radial size of the wafer is increased to provide greater yield of integrated circuit devices to be fabricated per substrate, the difficulty of obtaining uniformity over the entire wafer becomes correspondingly more severe. Since device yield is directly proportional to the degree of uniformity obtained, the art of machine design is advanced to the same degree that substrate surface processing uniformity may be improved.
The utility of the heretofore known reactors in either the diode or triode electrode configurations has been further limited in respect to the pressures at which selected ion-dominated and chemically-dominated processing were able to be efficiently run on semiconductor wafers and other substrates. In the application to VLSI, where, for example, it is desirable to fabricate microstructures with ever smaller features, the fineness and scale of the detail able to be fabricated depends on the pressure in the reactors. As the pressures are reduced at which the selected ion-dominated and chemically-dominated processes are run, the fineness and scale of the microstructures able to be fabricated thereby are correspondingly increased. However, below a certain pressure, about seventy (70) mTorr for the reactors in the triode configuration and about eight hundred (800) mTorr for the reactors in the diode configuration, the efficiency of the heretofore known substrate surface processing apparatus became too low to provide practicable processing, which has "frozen" the fineness and scale of the microstructures that have heretofore been able to be fabricated at levels that are larger and coarser than what are otherwise desirable. Since the degree of fineness and scale of the microstructures able to be fabricated is inversely proportional to the pressure level in these reactors, the art of machine design is advanced to the same degree that lower pressure processing may be able to be efficiently obtained.